Thin film transistor-liquid crystal display (TFT-LCD) uses a change of electric field strength on a liquid crystal layer to change a degree of rotation of liquid crystal molecules and control the light intensity, thereby to display an image. Generally, a complete liquid crystal panel must comprise a backlight module, a polarizer, an upper substrate (usually a color film substrate), a lower substrate (usually an array substrate), and a liquid crystal molecules layer arranged in a cell formed by the two substrates.
Crisscross data lines and gate lines are formed on the array substrate, and pixel units arranged in a matrix form are formed by the data lines and gate lines. Each pixel unit includes a TFT switch and a pixel electrode. The TFT switch includes a gate electrode, a source electrode, a drain electrode and an active layer. The gate electrode is connected to the gate line, the source electrode is connected to the data line, the drain electrode is connected to the pixel electrode, and the active layer is arranged between the source/drain electrode and the gate electrode.
Usually, a common electrode is further formed on the array substrate and configured to form an electric field with the pixel electrode. The degree of rotation of the liquid crystal molecules depends on the change of electric field strength between the common electrode and the pixel electrode.
For Advanced super dimension switch (ADS-DS, ADS for short), it refers to the formation of a multi-dimensional electric field through electric fields generated at edges of slit electrodes in an identical plane and an electric field generated between a slit electrode layer and a plate electrode layer, so as to rotate all orientational liquid crystal molecules between the slit electrodes and right above the electrodes in a liquid crystal cell, thereby to improve the working efficiency of the liquid crystal molecules and increase the light transmittance. A TFT-LCD product using the ADS technology can provide excellent image quality, and meanwhile has such advantages as a high resolution, high light transmittance, low power consumption, a wide view angle, a high aperture ratio, low chromatic aberration, and no push Mura.
As shown in FIG. 1, storage capacitance (Cst) between a common electrode 11 and a pixel electrode 112 in a TFT array substrate 110 in an ADS mode is very large, the storage capacitor almost occupies the entire pixel region. Especially for a large-scale product, when an area of the pixel region becomes bigger, the storage capacitance is much larger. Usually, in order to fit to such large storage capacitance, it is required to design a bigger TFT to fill therein. However, such a TFT occupies the pixel region, and coupling capacitance Cgd, Cgs of the TFT itself also become larger, so the image display is adversely affected and the design thereof is limited. Generally, one of the most direct ways to solve this problem is to form the ADS-type pixel electrode 112 and the common electrode 111 in the state as shown in FIG. 2. However, such a structure cannot be directly implemented by an existing process. This is because both the pixel electrode 112 and the common electrode 111 are transparent, and during the exposing and developing procedures using a device, an alignment effect of transparent films is limited, i.e., it is impossible to use the device to obtain the real structure as shown in FIG. 2. If the relative displacement of the pixel electrode and the common electrode is uneven within an active display region due to the alignment deviation, e.g., if the pixel electrode 112 at some region is offset to the left relative to the common electrode 111 while the pixel electrode 112 at another region is offset to the right relative to the common electrode 111, there is unequal gaps between Cst regions. As a result, in an image, uneven display grayscale occurs among the regions of the display device, and a distorted image is seen by eyes due to the uneven display brightness between the regions. This is a serious display defect, but there is no perfect solution for this in the prior art.